Adaugat la data: 2010-09-03
de catre: danutza
Numar pagini: 14
Tip document: .doc
Nivel: Facultate
Dimensiune: 291.5 KB
Downloads: 0
Credite: 0

Din referat: Color About Vision Deficiency

Color Blindness (Color About Vision Deficiency) 

What colorblindness is:

•    Color blindness (color vision deficiency) is a condition in which certain colors cannot be distinguished, and is most commonly due to an inherited condition.

Red/Green color blindness is by far the most common form, about 99%, and causes problems in distinguishing reds and greens.

Another color deficiency Blue/Yellow also exists, but is rare and there is no commonly available test for it.

•    Depending on just which figures you believe, color blindness seems to occur in about 8% - 12% of males of European origin and about one-half of 1% of females.

I did not find any figures for frequency in other races. Total color blindness (seeing in only shades of gray) is extremely rare.

•    There is no treatment for color blindness, nor is it usually the cause of any significant disability. However, it can be very frustrating for individuals affected by it.

Those who are not color blind seem to have the misconception that color blindness means that a color blind person sees only in black and white or shades of gray.

While this sort of condition is possible, it is extremely rare. Being color blind does keep one from performing certain jobs and makes others difficult.

Life's minor frustrations (and occasional dangers) for the color blind:

•    Weather forecasts - especially the Weather Channel - where certain colors just can not be distinguished on their weather maps. Also, maps in general because of the color coding on the legends.

•    Bi-color and tri-color LEDs (Light Emitting Diodes): Is that glowing indicator light red, yellow, or green?

•    Traffic lights, and worst of all, Caution lights: Color blind people always know the position of the colors on the traffic light - in most states, Red on top, Yellow in the center, Green (or is that blue?) on the bottom.

It isn't good when we go to a city or state where they put traffic lights horizontal - it takes a couple of days to get used to that one! But caution lights present an entirely different problem.

In this situation there is only one light; no top or bottom, no right or left, just one light that is either red or yellow - but which is it?

•    Getting in the sun with your girlfriend: So, you're out in the boat or on the beach with your girlfriend and soaking up the rays.

But I can't tell until far too late if I'm getting red - or if she is. If I can tell it's red, by that time it's fire engine red and a painful sunburn is already present.

•    Color observation by others: "Look at those lovely pink flowers on that shrub". My reply, looking at a greenish shrub "What flowers?"

•    Purchasing clothing: I've got some really neat colors of clothes. Not everyone appreciates them like I do though; they seem to think the colors are strange. I just don't know why!

•    Kids and crayons: Color vision deficiencies bother affected children from the earliest years. At school, coloring can become a difficulty when one has to take the blue crayon -and not the pink one- to color the ocean.

•    Test strips for hard water, pH, swimming pools, etc.: A color blind person is generally unable to :

o    interpret some chemical reactions

o    see that litmus paper turns red by acid

o    identify a material by the color of its flame such as lead blue or potassium purple

o    interpret the chemical testing kits for swimming pool water, test strips for hard water, soil or water pH tests - all of which rely on subtle color differences and a band of similar colors to compare against.

•    Cooking and foods:

o    When cooking, red deficient individuals cannot tell whether their piece of meat is raw or well done.

Many can not tell the difference between green and ripe tomatoes or between ketchup and chocolate syrup.

o    Some food can even look definitely disgusting to color deficient individuals.

For example, people with a green deficiency cannot possibly eat spinach which to them just look like cow pat.

They can however distinguish some citrus fruits.

Oranges seem to be of a brighter yellow than that of lemons.

•    Are you wearing lipstick? Many color blind people cannot tell whether a woman is wearing lipstick or not.

More difficult to handle for some is the inability to make the difference between a blue-eyed blonde and a green-eyed redhead.

Clinical information about color blindness:

•    Cones (color sensitive receptors) containing single visual pigments selective for red, green, and blue light, are present in the normal human eye.

Disturbances of color vision will occur if the amount of pigment per cone is reduced or if one or more of the three cone systems are absent.

•    Although defective color vision may be acquired as a result of another eye disorder, the vast majority of color blind cases are hereditary - present at birth. The gene for this is carried in the X chromosome.

Since males have an X-Y pairing and females have X-X, color blindness can occur much more easily in males and is typically passed to them by their mothers.

•    Color blindness is rooted in the chromosomal differences between males and females. Females may be carriers of color blindness, but males are more commonly affected.

•    Color blindness is a malfunction of the retina, which converts light energy into electircal energy that is then transmitted to the brain. This conversion is accomplished by two types of photoreceptor cells in the retina: rods and cones.

•    The cones are responsible for encoding color. Each cone contains structures or visual pigments sensitive to one of three wavelengths of light: red, green, and blue.

Normal persons are able to match all colors of the spectrum by mixtures of only three fundamental color sensitivities. Hence, the huge variety of colors we perceive stems from the cone cells' response to different compositions of wavelengths of light.

•    Defects in color vision occur when one of the three cone cell color coding structures fails to function properly. One of the visual pigments may be present and functioning abnormally, or it may be absent altogether.

•    For practical purposes, all color-deficient individuals have varieties of red or green deficiency. Blue deficiencies are very rare. Color deficient patients are not completely red or green blind.

Compared to persons with normal color vision, they have some trouble differentiating between certain colors, but the severity of the color deficiency is variable.

•    Color blindness is normally diagnosed through clinical testing. (See the Ishihara color test - the one most common test used) Although there is no treatment for color blindness, most color deficient persons compensate well for their defect and may even discover instances in which they can discern details and images that would escape normal-sighted persons.

At one time the U.S. Army found that color blind persons can spot "camouflage" colors where those with normal color vision are fooled by it.

How color blindness works:

•    The human eye sees by light stimulating the retina (a neuro-membrane lining the inside back of the eye).

The retina is made up of what are called Rods and Cones. The rods, located in the peripheral retina, give us our night vision, but can not distinguish color.

Cones, located in the center of the retina (called the macula), are not much good at night but do let us perceive color during daylight conditions.

•    Many people think anyone labeled as "colorblind" only sees black and white - like watching a black and white movie or television.

This is a big misconception and not true. It is extremely rare to be totally color blind. There are many different types and degrees of colorblindness, really they are "color deficiencies" since virtually no one is truly blind to all colors.

•    People with normal cones and color vision are able to see all the different colors and subtle mixtures of them by using cones sensitive to one of three wavelength of light - red, green, and blue.

•    A mild color deficiency is present when one or more of the three cones functions "poorly". A more severe color deficiency is present when one of the cones does not function at "all" or is missing.

•    Protanomaly (one out of 100 males):

Protanomaly is referred to as "red-weakness", an apt description of this form of color deficiency.

Any redness seen in a color by a normal observer is seen more weakly by the protanomalous viewer, both in terms of its "coloring power" (saturation, or depth of color) and its brightness.

Red, orange, yellow, yellow-green, and green, appear somewhat shifted in hue ("hue" is just another word for "color") towards green, and all appear paler than they do to the normal observer.

The redness component that a normal observer sees in a violet or lavender color is so weakened for the protanomalous observer that he may fail to detect it, and therefore sees only the blue component.

Hence, to him the color that normals call "violet" may look only like another shade of blue.